I bought two pairs for the cable trolley. The idea was to place a heavy roller between two bars that are free to rotate using PGN bearings. So far, so good. They work well and are easy to set up. The only problem is that they don't turn easily but are quite stiff. There are no instructions on how to lubricate them and how to just start them. I ended up using some bike chain lube and it helped a little but still didn't spin as freely as expected. Update: I have ordered a grease gun and will make adjustments as the situation changes.